This invention relates to the treatment of hydrocarbon oils and, more particularly, to the hydroconversion of heavy hydrocarbon oils in the presence of particulate additives for inhibiting coke formation.
Hydroconversion processes for the conversion of heavy hydrocarbon oils to light and intermediate naphthas of good quality for reforming feedstocks, fuel oil and gas oil are well known. These heavy hydrocarbon oils can be such materials as petroleum crude oil, atmospheric tar bottoms products, vacuum tar bottoms products, heavy cycle oils, shale oils, coal derived liquids, crude oil residuum, topped crude oils and the heavy bituminous oils extracted from oil sands. Of particular interest are the oils extracted from oil sands and which contain wide boiling range materials from naphthas through kerosene, gas oil, pitch, etc., and which contain a large portion of material boiling above 524.degree. C. equivalent atmospheric boiling point.
As the reserves of conventional crude oils decline, these heavy oils must be upgraded to meet the demands. In this upgrading, the heavier materials is converted to lighter fractions and most of the sulphur, nitrogen and metals must be removed.
This can be done either by a coking process, such as delayed of fluidized coking, or by a hydrogen addition process such as thermal or catalytic hydrocracking. The distillate yield from the coking process is typically about 80 wt. % and this process also yields substantial amounts of coke as by-product.
Work has also been done on an alternate processing route involving hydrogen addition at high pressures and temperatures and this has been found to be quite promising. In this process, hydrogen and heavy oil are pumped upwardly through an empty tubular reactor in the absence of any catalyst. It has been found that the high molecular weight compounds hydrogenate and/or hydrocrack into lower boiling ranges. Simultaneous desulphurization, demetallization and denitrogenation reactions take place.
Work has been done to develop additives which can suppress coking reaction or can remove the coke from the reactor. It has been shown in Ternan et al., Canadian Patent No. 1,073,389, issued Mar. 10, 1980 and Ranganathan et al., U.S. Pat. No. 4,214,977, issued Jul. 29, 1980, that the addition of coal or coal-based additive results in the reduction of coke deposition during hydrocracking. The coal additives act as sites for the deposition of coke precursors and thus provide a mechanism for their removal from the system.
Ternan et al., Canadian Patent No. 1,077,917 describes a process for the hydroconversion of a heavy hydrocarbonaceous oil in the presence of a catalyst prepared in situ from trace amounts of metals added to the oil as oil soluble metal compounds.
In U.S. Pat. No. 3,775,286, a process is described for hydrogenating coal in which the coal was either impregnated with hydrated iron oxide or dry hydrated iron oxide powder was physically mixed with powdered coal. Canadian Patent No. 1,202,588 describes a process for hydrocracking heavy oils in the presence of an additive in the form of a dry mixture of coal and an iron salt, such as iron sulphate.
Fly ash is described as a useful additive for suppressing coke formation in U.S. Pat. No. 4,299,685 and pyrite as a particulate additive is described in Canadian Patent 1,152,925.
Development of such additives has allowed the reduction of reactor operating pressure without coking reaction. However the injection of large amounts of fine additive is costly, and the application is limited by the incipient coking temperature, at which point mesophase (a pre-coke material) is formed in increasing amounts.
Further, it is shown in Jain et al., U.S. Pat. No. 4,969,988 that conversion can be further increased through reduction of gas hold-up by injecting an anti-foaming agent, preferably into the top section of the reactor.
Sears et al., U.S. Pat. No. 5,374,348 teaches recycle of heavy vacuum fractionator bottoms to the reactor to reduce overall additive consumption by 40% more.
It is the object of the present invention to provide a process for hydrocracking heavy hydrocarbon oils using additive particles in the feedstock to suppress coke formation in which improved yields can be achieved by increased reaction temperatures facilitated by increased nitrogen levels in the reaction zone.